The study, published in Cell Metabolism, reports that short term increases in dietary nitrates can boost muscle efficiency during exercise, and finds that the that the improved performance is linked to increased efficiency of the mitochondria that power our cells.
Mitochondrial efficiency is usually measured as the amount of oxygen consumed per adenosine triphosphate (ATP) produced – a measure known as the P/O ratio. The new study shows that nitrate “has profound effects on basal human mitochondrial function as well as whole-body oxygen consumption during exercise.”
“In the current study we found a 19 percent increase in P/O ratio after nitrate supplementation. To our knowledge, there are no other dietary regimes described that have this effect,” said the researchers, led by Professor Eddie Weitzberg from the Karolinska Institutet, Sweden.
“Intriguingly, there was a strong correlation between the reduction in whole-body oxygen consumption during cycling and the increase in P/O ratio, which clearly suggests that a large part of the improved exercise efficiency is taking place at the mitochondrial level,” he added.
Until recently nitrate – which is abundant in green leafy vegetables – had been considered merely as an inert end product of nitric oxide (NO) metabolism or as a potentially toxic constituent in our diet.
However, the last decade has brought understanding of its importance in biological processes, including regulation of blood flow, blood pressure, cellular signaling, glucose homeostasis, and tissue responses to low oxygen levels (hypoxia).
Previous research has also linked nitrate rich foods and beverages, like beetroot juice, to improvements physiological benefits – including improved endurance. Such benefits have been shown to be, at least in part, due to a reduction in the ‘oxygen cost’ of exercise for healthy individuals after short-term dietary supplementation with nitrate.
Weitzberg and colleagues noted that the findings point toward the mitochondria (the ‘energy factories’ of cells) as a possible target for the effects of nitrate – suggesting that the production of ATP (an important transporter of chemical energy) may become more efficient. However, such mechanisms remain unclear and relatively unknown.
The new study, a double-blind crossover trial, studied the effects of a dietary intervention with inorganic nitrate on mitochondrial function and whole-body oxygen consumption in healthy volunteers.
Skeletal muscle biopsies were in conjunction with bicycle exercise tests were used to study the effects of dietary nitrate on mitochondrial efficiency and biochemical parameters, in addition to the expression of proteins involved in energy transfer.
The researchers reported that after taking a small dose of inorganic nitrate for three days volunteers consumed less oxygen while riding an exercise bike.
They said that skeletal muscle mitochondria after nitrate supplementation showed an improvement in efficiency (P/O ratio), which was strongly correlated to the reduction in oxygen cost during exercise.
These effects were found to accompany a reduction in ANT – an important protein involved in mitochondrial energy production.
“The fact that the relatively short term dietary regimen can influence expression of important mitochondrial proteins may have profound impact on exercise physiology,” said Weitzberg.
“Moreover, it may also have implications for metabolic and cardiovascular diseases in which dysfunctional mitochondria play a central role,” he added.
Weitzberg said that the “natural next step” is to repeat the experiment in people with conditions linked to mitochondrial dysfunction, including diabetes and cardiovascular disease, to see if they too enjoy such positive results.
He added that further studies to identify the molecular mechanisms and signaling pathways by which nitrate affects mitochondrial efficiency are clearly needed.
In an accompanying editorial Dr Sreekumaran Nair and his colleagues from the Mayo Clinic, note that the study provides strong evidence that short-term dietary nitrate supplementation enhances mitochondrial efficiency and enhances exercise performance. However they added that future studies should also address the impact of nitrates on mitochondrial reactive oxygen species (ROS) production.
“It is difficult to ignore the possibility that improved coupling may lead to increased ROS production rates, which may have an adverse effect on proteins, DNA, and cellular functions,” they said.
Source: Cell Metabolism
olume 13, Issue 2, Pages 149-159, doi: 10.1016/j.cmet.2011.01.004
“Dietary Inorganic Nitrate Improves Mitochondrial Efficiency in Humans”
Authors: F.J. Larsen, T.A. Schiffer, S. Borniquel, K. Sahlin, B. Ekblom, J.O. Lundberg, E. Weitzberg
Source: Cell Metabolism
Volume 13, Issue 2, Pages 117-118, doi: 10.1016/j.cmet.2011.01.013
“Can Dietary Nitrates Enhance the Efficiency of Mitochondria?”
Authors: K.S. Nair, B.A. Irving, I.R. Lanza